A polymeric solid electrolyte is a kind of polymeric thin film performing ion conduction rather than electron conduction. The polymeric solid electrolyte is adapted to be used in a series of primary and secondary lithium batteries or lithium-ion batteries to thin the batteries in shape. The thinned batteries can also be further processed into windable batteries, bipolar stack batteries, thin-film batteries, etc., according to various requirements. In addition, the use of polymeric solid electrolytes in the batteries can overcome the problems of difficult package and current leakage encountered by general batteries with liquid electrolyte.
In earlier stage, the research on polymeric solid electrolytes is focused on the complex film of polyethylene oxide (PEO) based material and a lithium salt. The material has a relatively low conductivity, as low as 10.sup.-7 .about.10.sup.-8 S/cm at room temperature, so that the material works only at high temperature such as 80.degree. C. or above. Furthermore, a lot of organic solvent which is detrimental to the industrial security and the environmental protection is used and then evaporated in the process for producing the polyethylene oxide based thin film.
In recent years, gel electrolytes, such as polyacrylonitrile (PAN) based electrolytes, have been reported to be used in cells, and the product has a practically desired level of conductivity at room temperature. Nevertheless, the film has to be produced in a glove box or dry room so that the manufacturing process will be built with high cost.
In addition, B. J. Bauer et al. claimed in U.S. Pat. No. 4,654,279 that a two phase interpenetrating network of a mechanical supporting phase of a continuous network of a crosslinked polymer and an ionic conducting phase comprising a metal salt complexing liquid polymer. The conductivities of these polymeric electrolytes are constrained by the characteristics of liquid polymer, which are approximating 10.sup.-4 S/cm, too low to be used in lithium batteries.
On the other hand, in the parent application, a composite electrolyte based on a WPU-PEO film containing therein an organic liquid electrolyte is disclosed. The material WPU in the invention plays the role of a mechanical supporting matrix, and the material PEO functions as an electrolyte absorbent. The conductivity of these electrolytes can be promoted to .about.10.sup.-3 S cm.sup.-1 at room temperature.